Cropping refers to the identification and/or removal of an area from an image. Typically such image manipulation is manually performed to remove unwanted subject material from the image to improve the overall composition of the image, or to emphasize a certain set of subject matter. For example, cropping a portrait image may emphasize a person's facial features whereas cropping an image containing a person playing a musical instrument may feature more than just the person's face. Such a cropped image may include additional subject matter, such as a portion, or the entire musical instrument. Cropping is also performed to compensate between different aspect ratios. For example a widescreen 16:9 format may be desired to showcase a landscape image of a mountain range that was originally taken in a 4:3 aspect ratio.
The cropping of a photographic image can be very subjective. However, there are a number of standard compositional rules that can be employed to select the area to be cropped. The “rule of thirds” dictates that an image is divided into nine equal parts with two equally-spaced horizontal lines and two equally-spaced vertical lines, where the important composition elements should be placed along the lines or at their intersections. Other rules include symmetrical balance, asymmetrical balance, radial balance, and simplicity. However, these rules require an artistic judgment of what rule to apply when as well as an artistic decision of what elements are to be included within the final cropped image.